Vehicle steering device

ABSTRACT

A vehicle steering device includes a steering shaft; a rotation operating member of the steering shaft; an operation-side motor that supplies an operating reaction force to the rotation operating member; a steering member; a steering-side motor that supplies an operating reaction force to the steering member; a steering angle detecting means that detects a steering angle; and a control means, an absolute angle detecting means is provided at the steering shaft, and a motor rotation angle detecting means is provided at a motor shaft of the operation-side motor.

This application claims the benefit of priority to Japanese PatentApplication No. 2004-152031 filed on May 21, 2004 and 2004-206084 filedon Jul. 13, 2004, both herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle steering device of a by-wiremethod, and more particularly, to means that makes smooth the control ofdriving for an operation-side motor, which supplies an operatingreaction force to a rotation operating member.

2. Description of the Related Art

In the related art, a vehicle steering device of a mechanical method inwhich a steering shaft is connected with a steering member via amechanical power transmission mechanism, has been used as a vehiclesteering device. However, in recent years, a vehicle steering device ofthe by-wire method is proposed, which converts the rotation state of asteering shaft into electric signals, and controls the driving of asteering-side motor provided at a steering member based on the electricsignals, and controls the driving of an operation-side motor thatsupplies an operating reaction force to a rotation operating member ofthe steering shaft, and supplies a desired operating reaction force tothe rotation operating member.

FIG. 6 is a structure view showing an example of a vehicle steeringdevice of the by-wire method, which has been conventionally proposed.The vehicle steering device includes a steering shaft 1; a rotationoperating member 2 such as a steering wheel that is operated to rotatethe steering shaft 1; an absolute operation angle detecting means 3,whose rotating portion is attached to the steering shaft 1, and whichdetects the absolute operation angle of the rotation operating member 2;an operation-side motor 4 that supplies an operating reaction force tothe rotation operating member 2 via the steering shaft 1; a speedreduction mechanism 5 which is interposed between the steering shaft 1and the operation-side motor 4 to reduce the operating reaction forcegenerated at the operation-side motor 4 and to transmit it to thesteering shaft 1; a steering shaft 7 provided at a transmissionmechanism 6, a steering-side motor 8 that rotates the steering shaft 7;a steering angle detecting means 9 that detects a steering angle, and acontrol means 10 that generates driving signals M1 for theoperation-side motor 4 and driving signals M2 for the steering-sidemotor 8 based on absolute operation angle signals θ1 outputted from theabsolute operation angle detecting means 3 and steering angle signals θ2outputted from the steering angle detecting means 9. Meanwhile, thetransmission mechanism 6 is constituted with a pinion gear 11 fixed tothe steering shaft 7, a rack shaft 12 having a rack gear engaging withthe pinion gear 11, and a link mechanism 14 having an axle 13 driven bythe rack gear 12 (for example, see Japanese Patent UnexaminedApplication Publication No. 2003-252223).

The control means 10 generates and outputs driving signals M1 for theoperation-side motor 4 based on the absolute operation angle signals θ1and the steering angle signals θ2. Therefore, like the vehicle steeringdevice of the mechanical method, the rotation operating member 2 can besupplied with operating reaction force according to the operating angleand direction of the rotation operating member 2. Also, the controlmeans 10 generates driving signals M2 for the steering-side motor 8based on the absolute operation angle signals θ1 and the steering anglesignals θ2, and outputs them. Therefore, like the vehicle steeringmember of the mechanical method, the steering member 6 can be steered inaccordance with the operating angle and direction of the rotationoperating member 2, and road state, etc.

However, in order to supply the rotation operating member 2 with smoothand continuous operating reaction force, that is, a force that does notcause a driver to feel uncomfortable in controlling the driving of theoperation-side motor 4, it is required to control the driving smoothlyor with high resolution. Also, in order to control the driving smoothlyor with high resolution, a detecting means having high resolution isrequired.

However, the detecting means having high resolution enough to performsmooth driving control usually has a high price or a low durability,therefore, it is difficult to control the driving of the operation-sidemotor smoothly.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problems, and anobject of the invention is to smoothly control the driving for theoperation-side motor.

In order to solve the problem, a vehicle steering device according to anaspect of the present invention includes a rotation operating memberthat is operated to rotate the steering shaft; an absolute operationangle detecting means that detects an absolute operation angle of therotation operating member; an operation-side motor that supplies anoperating reaction force to the rotation operating member; a speedreduction mechanism interposed between a motor shaft of theoperation-side motor and the steering shaft to reduce the rotation speedof the motor shaft and to transmit the reduced rotation to the steeringshaft; a motor rotation angle detecting means provided at the motorshaft of the operation-side motor to detect the rotation angle of theoperation-side motor; a steering-side motor that changes a steeringangle via a transmission mechanism; a steering angle detecting meansthat detects the steering angle; and a control means that controls thedriving of the steering-side motor based on the steering angle and theabsolute operation angle of the rotation operating member, and alsocontrols the driving of the steering-side motor based on the steeringangle and the rotation angle of the operation-side motor.

If a rotation angle detecting means is provided at the motor shaft ofthe operation-side motor, the rotation speed of the rotation operatingmember is increased and transmitted to the motor shaft of theoperation-side motor by the speed reduction mechanism provided betweenthe steering shaft and the motor shaft. Therefore, high resolutionabsolute operation angle signals can be obtained without providing anangle detecting means having high resolution, and the driving of theoperation-side motor can be controlled smoothly.

In addition, preferably, the absolute operation angle detecting means isindependently provided to be driven directly by the steering shaft, notvia the speed reduction mechanism, and the motor rotation angledetecting means is constituted with a relative rotation angle detectingmeans directly driven by the motor shaft and an absolute rotation anglecomputing means that computes the absolute rotation angle of theoperation-side motor from the absolute operation angle of the rotationoperating member and the relative rotation angle of the operation-sidemotor, and the control means controls the driving of the operation-sidemotor based on the absolute rotation angle.

In order to compute the absolute rotation angle of the operation-sidemotor, a reference rotation angle as well as the relative rotation angleis required. However, the absolute operation angle of the rotationoperating member is used as the reference operation angle withoutproviding a reference rotation angle detecting means. Therefore, theabsolute rotation angle detecting means can be omitted, and the cost ofthe vehicle steering device can be decreased.

Also, preferably, the control means controls the driving of thesteering-side motor by using the rotation angle of the operation-sidemotor as the absolute operation angle, and the motor rotation angledetecting means also functions as the absolute operation angle detectingmeans.

It is not necessary to provide a separate absolute operation angle meansthat detects the absolute operation angle of the rotation operatingmember. Therefore, the cost of the vehicle steering device can bedecreased.

In addition, preferably, the vehicle steering device according to theaspect of the present invention includes a signal converting means thatconverts rotation angle signals outputted from the motor rotation angledetecting means into signals of a type that the control means requires,and then supplies them to the control means.

Also, preferably, the vehicle steering device according to the aspect ofthe present invention includes a signal converting means that convertsthe driving signals for the operation-side motor outputted from thecontrol means into signals of a type that the operation-side motorrequires, and then transmits them to the operation-side motor.

Various control means that processes different types of signalsaccording to vehicle manufactures or vehicle types etc. can be providedto vehicles. In the related art, respective vehicle steering devices fitto control means are manufactured by different vehicle steering devicemanufacturers. In this case, the manufacturing line becomes complicated,and the cost of the vehicle steering device becomes high. Contrary tothis, when a signal converting means that converts the operation anglesignals outputted from the operation angle detecting means into signalsof a type that the control means requires, and then transmits them tothe control means, and converts the driving signals for theoperation-side motor outputted from the control means into signals of atype that the operation-side motor requires, and then transmits them tothe operation-side motor, the operation angle detecting means, theoperation-side motor and the control means can be shared. Therefore, thevehicle steering cost can be decreased.

According to the aspect of the present invention, when the motorrotation angle detecting means is provided at the motor shaft of theoperation-side motor, the rotation speed of the rotation operatingmember is increased by the speed reduction mechanism provided betweenthe steering shaft and the motor shaft, and then transmitted to themotor shaft of the operation-side motor. Therefore, high resolutionabsolute operation angle signals can be obtained without providing anangle detecting means having high resolution, and the driving of theoperation-side motor can be controlled smoothly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the structure of a vehicle steering device accordingto an embodiment;

FIG. 2 is a graph comparing the output characteristics of a motorrotation angle detecting means with the output characteristics of anabsolute operation angle detecting means;

FIG. 3 illustrates the structure of a vehicle steering device accordingto a second embodiment;

FIG. 4 illustrates the structure of a vehicle steering device accordingto a third embodiment;

FIG. 5 illustrates the structure of a vehicle steering device accordingto a fourth embodiment; and

FIG. 6 illustrates the structure of a vehicle steering device in therelated art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of a vehicle steering deviceaccording to the present invention will be described with reference toFIGS. 1 to 5. FIG. 1 illustrates the structure of a vehicle steeringdevice according to a first embodiment, and FIG. 2 is a graph comparingthe output characteristics of a motor rotation angle detecting meanswith the output characteristics of an absolute operation angle detectingmeans, and FIG. 3 illustrates the structure of a vehicle steering deviceaccording to a second embodiment. FIG. 4 illustrates the structure of avehicle steering device according to a third embodiment. FIG. 5illustrates the structure of a vehicle steering device according to afourth embodiment.

As can be apparent from the comparison between FIG. 1 and FIG. 6, thevehicle steering device according to the first embodiment furtherincludes a motor rotation angle detecting means 20 that detects themotor rotation angle of an operation-side motor 4 and an absolute anglecomputing means 21 that computes an absolute motor rotation angle signalθa for the operation-side motor 4 based on a motor rotation angle signalθr of the operation-side motor 4 outputted from the motor rotation angledetecting means 20 and an absolute operation angle signal θ1 of arotation operating member 2 outputted from an absolute operation angledetecting means 3 comparing with a vehicle steering device in therelated art shown in FIG. 6.

The other parts except the above are the same as those of the vehiclesteering device in the related art shown in FIG. 6, that is, thereference numeral 1 represents a steering shaft, the reference numeral 2represents a rotation operating member, the reference numeral 3represents an absolute operation angle detecting means, the referencenumeral 4 represents an operation-side motor, the reference numeral 5represents a speed reduction mechanism, the reference numeral 6represents a steering member, the reference numeral 7 represents asteering shaft, the reference numeral 8 represents a steering-sidemotor, the reference numeral 9 represents a steering angle detectingmeans, and the reference numeral 10 represents a control means. Also,the steering member 6 is constituted with a pinion gear 11 fixed to thesteering shaft 7, a rack shaft 12 having a rack gear that engages thepinion gear 11, and a link mechanism 14 including an axle 13 driven bythe rack shaft 12.

As the absolute operation angle detecting means 3, a digital encoder, ananalog potentiometer or the like that detects the absolute rotationangle of the steering shaft 1 can be used. When an encoder is used asthe absolute operation angle detecting means 3, for example, a codeplate on which a code pattern is formed is attached to the steeringshaft 1, and when a potentiometer is used as the absolute operationangle detecting means 3, for example, a resistive substrate on which aresistive pattern is formed or a rotary plate to which a slider isattached is attached to the steering shaft 1.

Contrary to this, in this embodiment, a digital encoder that detects therelative motor rotation angle of the operation-side motor 4 is used asthe motor rotation angle detecting means 20. The code plate on which acode pattern is formed is attached to the motor shaft 4 a of theoperation-side motor 4.

The absolute angle computing means 21 computes the absolute rotationangle θa by adding or subtracting the relative rotation angle signal θrof the operation-side motor 4 outputted from the motor rotation angledetecting means 20 to or from a reference rotation angle, which is theabsolute operation angle signal θ1 of the rotation operating member 2outputted from the absolute operation angle means 3 when an ignitionswitch is turned on.

The control means 10 generates driving signals M1 for the operation-sidemotor 4 based on the absolute rotation angle θa outputted from theabsolute angle computing means 21 and the steering angle signals θ2outputted from the steering angle detecting means 9, and controls thedriving of the operation-side motor 4. Also, it generates drivingsignals M2 for the steering-side motor 8 based on the absolute operationangle signal θ1 of the rotation operating member 2 outputted from theabsolute operation angle detecting means 3 and the steering anglesignals θ2 outputted from the steering angle detecting means 8, andcontrols the driving of the steering-side motor 8.

Since the speed reduction mechanism 5 interposed between the steeringshaft 1 and the operation-side motor 4 reduces an operating reactionforce generated at the operation-side motor 4, and then transmits it tothe steering shaft 1, the speed reduction mechanism 5 acts as a speedincrease mechanism for the motor rotation angle detecting means 20 whenthe rotating portion of the rotation angle detecting means 20 is coupledwith the motor shaft 4 a of the operation-side motor 4. Therefore, whenthe motor rotation angle detecting means 20 is an encoder, the number ofthe codes of the motor rotation angle signals θ_(r) to the unit rotationangle of the rotation operating member 2 increases as much as the speedincrease ratio of the speed reduction mechanism 5 more than the numberof the codes of the operation angle signals θ1. Therefore, if thecontrol means 10 generates driving signals M1 for the motor of operation4 based on the absolute rotation angle θa outputted from the absoluteangle computing means 21, the driving of the operation-side motor 4 canbe controlled with high resolution, that is, more smoothly as comparedwith the case where the control means 10 generates driving signals M1for the motor of operation 4 based on the absolute operation anglesignals θ1 of the rotation operating member 2 outputted from theabsolute operation angle detecting means 3. Thus an operating reactionforce, which is smooth and continuous, not causing a driver to feeluncomfortable, can be provided to the rotation operating member 2.

Also, since the absolute operation angle signals θ1 outputted from theabsolute operation angle detecting means 3 is used as the referencerotation angle for computing the absolute rotation angle θa of theoperation-side motor 4, an additional detecting means is not required todetect the reference rotation angle, and the increase of the cost of thevehicle steering device can be suppressed.

Meanwhile, in the first embodiment, only a relative rotation angledetecting means is provided in the motor shaft 4 a of the operation-sidemotor 4, however, as shown in a second embodiment of FIG. 3, an absoluteangle detecting means constituted with a reference angle detecting means22 b and an absolute rotation angle computing means 22 c as well as therelative rotation angle detecting means 22 a can be provided in themotor shaft 4 a of the operation-side motor 4. Also, it is possible touse only an analog potentiometer as the absolute angle detecting means.

In addition, in the first embodiment, the rotating portion of the motorrotation angle detecting means 20 is directly attached to the motorshaft 4 a of the operation-side motor 4, however, a transmissionmechanism constituted with the combination of a large gear attached tothe motor shaft 4 a and a small gear attached to the rotating portioncan be provided additionally between the rotating portion of the motorrotation angle detecting means 20 and the motor shaft 4 a of theoperation-side motor 4.

FIG. 4 shows the structure of a vehicle steering device according to athird embodiment. The vehicle steering device includes a steering shaft1, a rotation operating member 2, a combined rotation angle detectingmeans and an absolute operation angle detecting means 50, anoperation-side motor 4, a speed reduction mechanism 5, a steering member6, a steering shaft of an axle 7, a steering-side motor 8, a steeringangle detecting means 9 and a control means 10. The steering member 6 isconstituted with a pinion gear 11 fixed to the steering shaft 7, a rackshaft 12 having a rack gear engaging with the pinion gear 11 and a linkmechanism 14 having an axle 13 driven by the rack shaft 12.

The steering device of the embodiment is characterized in that the motorrotation angle detecting means also functions as an absolute operationangle detecting means. In addition, as the combined motor operationangle detecting means and absolute operation angle detecting means 50, adigital encoder, an analog potentiometer or the like can be used. Whenan encoder is used as the combined motor operation angle detecting meansand absolute operation angle detecting means 50, a code plate on which acode pattern is formed is attached to the motor shaft 4 a of theoperation-side motor 4, and when a potentiometer is used as the combinedmotor operation angle detecting means and absolute operation angledetecting means 50, a resistive substrate on which a resistive patternis formed or a rotary plate to which a slider is attached is attached tothe motor shaft 4 a of the operation-side motor 4.

As described above, since the speed reduction mechanism 5 interposedbetween the steering shaft 1 and the operation-side motor 4 reduces anoperating reaction force generated at the operation-side motor 4, andthen transmits it to the steering shaft 1, the speed reduction mechanism5 acts as a speed increase mechanism to the combined motor operationangle detecting means and absolute operation angle detecting means 50when the rotating portion of the combined motor operation angledetecting means and absolute operation angle detecting means 50 iscoupled with the motor shaft 4 a of the operation-side motor 4.Therefore, when the combined motor operation angle detecting means andabsolute operation angle detecting means 50 is a potentiometer, thechanging amount of the absolute operation angle signals θ1 to the unitrotation angle of the rotation operating member 2 in the vehiclesteering device according to the embodiment increases as much as thespeed increase ratio of the speed reduction mechanism 5 more than thatof the vehicle steering device in the related art, in which the rotatingportion of the absolute operation angle detecting means 3 is attached tothe steering shaft 1. In addition, when the combined motor operationangle detecting means and absolute operation angle detecting means 50 isan encoder, as shown in FIG. 2, the number of the codes of the absoluteoperation angle signals θ1 to the unit rotation angle of the rotationoperating member 2 increases as much as the speed increase ratio of thespeed reduction mechanism 5. Therefore, the driving of theoperation-side motor 4 can be controlled with high resolution, that is,more smoothly. Thus an operating reaction force, which is smooth andcontinuous, not causing a driver to feel uncomfortable, can be providedto the rotation operating member 2.

In addition, in this embodiment, the control means 10 controls thedriving of the steering-side motor 8 using the rotation angle of theoperation-side motor 4 as the absolute operation angle of the rotationoperating member 2, and the motor rotation angle detecting means alsofunctions as the absolute operation angle detecting means that detectsthe absolute steering angle of the rotation operating member 2.Therefore, it is not required to provide an absolute operation angledetecting means that detects an absolute operation angle of the rotationoperating member 2, and the cost of the vehicle steering device can bedecreased.

Next, a vehicle steering device according to a fourth embodiment of thepresent invention will be described with reference to FIG. 5.

As shown in FIG. 5, the vehicle steering device is characterized byhaving a signal converting means between the combined motor operationangle detecting means and absolute operation angle detecting means 50and the operation-side motor 4, and the control means 10, which convertsthe absolute operation angle signals θ1 outputted from the combinedmotor operation angle detecting means and absolute operation angledetecting means 50 into the absolute operation angle signals θ1′ of atype that the control means 10 requires, and then transmits it to thecontrol means 10, and converts the driving signals M1′ for theoperation-side motor 4 outputted from the control means 10 into thedriving signals M1 of a type that the operation-side motor 4 requires,and then transmits them to the operation-side motor 4.

For example, when a device that outputs digital signals such as anencoder and the like is provided as the combined motor operation angledetecting means and absolute operation angle detecting means 50, and adevice that requires the input of analog signals is provided as thecontrol means, the signal converting means 15 converts digital absoluteoperation angle signals θ1 into analog absolute operation angle signalsθ1′, and then transmits them to the control means 10. Also, when adevice having a low resolution is provided as the combined motoroperation angle detecting means and absolute operation angle detectingmeans 50, and a device that requires the input of high resolutionsignals is provided as the control means, the signal converting means 15convert low resolution signals θ1 into high resolution signals θ1′, andthen transmits them to the control means 10. Further, when a small-sizedmotor having a low rated current is provided as the operation-side motor4, and a device that outputs motor driving signals fit to a large-sizedmotor having a large rated current is provided as the control means, thesignal converting means 15 converts large electric power signals M1′into small electric power signals M1, and then transmits them to theoperation-side motor 4. Even when the combined motor operation angledetecting means and absolute operation angle detecting means 50, theoperation-side motor 4 and the control means 10 have a reverserelationship to the above, the signal converting means 15 convertssignals.

As described above, since the vehicle steering device of the embodimentincludes the signal converting means 15, which converts the absoluteoperation angle signals θ1 outputted from the combined motor operationangle detecting means and absolute operation angle detecting means 50into the absolute operation angle signals θ1′ of a type that the controlmeans 10 requires, and then transmits it to the control means 10, andconverts the driving signals M1′ for the operation-side motor 4outputted from the control means 10 into the driving signals M1 of atype that the operation-side motor 4 requires, and then transmits themto the operation-side motor 4, the combined motor operation angledetecting means and absolute operation angle detecting means 50, theoperation-side motor 4 and the control means 10 can be shared.Therefore, the cost of the vehicle steering device can be decreased.

1. A vehicle steering device comprising: a rotation operating memberthat is operated to rotate a steering shaft; an absolute operation angledetecting means that detects an absolute operation angle of the rotationoperating member; an operation-side motor that supplies an operatingreaction force to the rotation operating member; a speed reductionmechanism interposed between a motor shaft of the operation-side motorand the steering shaft to reduce a rotation speed of the motor shaft andto transmit a reduced rotation to the steering shaft; a motor rotationangle detecting means provided at the motor shaft of the operation-sidemotor to detect a rotation angle of the operation-side motor; asteering-side motor that changes a steering angle via a transmissionmechanism; a steering angle detecting means that detects the steeringangle; and a control means that controls driving of the steering-sidemotor based on the steering angle and the absolute operation angle ofthe rotation operating member, and that controls driving of theoperation-side motor based on the steering angle and the rotation angleof the operation-side motor.
 2. The vehicle steering device according toclaim 1, wherein the absolute operation angle detecting means isindependently provided to be driven directly by the steering shaft, notvia the speed reduction mechanism, and the motor rotation angledetecting means is constituted with a relative rotation angle detectingmeans directly driven by the motor shaft and an absolute rotation anglecomputing means that computes the absolute rotation angle of theoperation-side motor from the absolute operation angle of the rotationoperating member and a relative rotation angle of the operation-sidemotor, and the control means controls the driving of the operation-sidemotor based on the absolute rotation angle.
 3. The vehicle steeringdevice according to claim 1, wherein the control means controls thedriving of the steering-side motor by using the rotation angle of theoperation-side motor as the absolute operation angle, and the motorrotation angle detecting means also functions as the absolute operationangle detecting means.
 4. The vehicle steering device according to claim1, further comprising: a signal converting means that converts rotationangle signals outputted from the motor rotation angle detecting meansinto signals that are recognizable to the control means, and suppliesthe signals to the control means.
 5. The vehicle steering deviceaccording to claim 1, further comprising: a signal converting means thatconverts driving signals for the operation-side motor outputted from thecontrol means into signals that are recognizable to the operation-sidemotor, and supplies the signals to the operation-side motor.